This invention relates, in general, to a method of forming electrical inductance coils and the electrical coils formed thereby which are particularly useful in providing the rotating in-plane magnetic field for the propagation of bubbles in bubble memories.
There are a number of prior patents relating to the formation of coils of various types by utilizing printed circuit techniques, typical examples of which are the U.S. patents to Shortt, et al., U.S. Pat. No. 3,002,260, Wilburn, U.S. Pat. No. 3,633,273 and other patents showing laminated sheet coils such as the Lohman U.S. Pat. No. 3,320,566 and in this general field a method of manufacturing electrical condensors with metalized coating on a paper strip is shown in the Dubilier U.S. Pat. No. 2,716,180. However, notwithstanding this prior art, there exists a requirement for an electrical coil which has a high packing coefficient, which is cost effective, and which has the additional advantage of allowing design choices, such as, changing the pitch of the coils to vary the induced magnetic field strength and to change the distributed capacitance of the coil.
These requirements for the coil, i.e., high packing coefficient, reduced costs, and choice of design are particularly important in the field of bubble memories where the in-plane magnetic field is produced by two or more coils surrounding a magnetic substrate capable of supporting bubbles therein. For a high packing coefficient, the thickness of the conductors which are formed into a coil must be small if the package is to be small and the coils brought close to this magnetic substrate and for cost effectiveness the coils can be formed utilizing printed circuit techniques along with other items made for bubble memories using these same techniques.
Accordingly, it is a primary object of this invention to provide a new and improved method of forming a magnetic coil.
A second object of this invention is to provide a new and improved coil of reduced thickness to provide a smaller cross-sectional area and to bring the coil closer to the item being subjected to the induced magnetic field.
Still another object of this invention is to provide a cost effective coil which still meets the foregoing objects.
Still another object of this invention is to provide a coil which allows a choice of design such as the change of pitch to vary the induced magnetic field strength in different areas of the coil and to change the distributed capacitor characteristics of the coil.
Another advantage will be apparent to those skilled in the art on a reading of the following description of the invention in that this coil, and the method of making same, may be utilized where the core or sub-assembly about which the coil is to be placed will not permit the utilization of a prewound or preformed coil. The present invention overcomes this deficiency by being able to be formed in place over the coil or subassembly.
Accordingly, still another object of this invention is to provide a coil and the method of making same where the coil may be formed in place over the core or sub-assembly thereby overcoming a deficiency of preformed coils.